The light show far below

 kw: book reviews, nonfiction, oceanography, bioluminescence, memoirs, giant squid, architeuthis

When I lived in southern California I frequently went to the beach; my favorites were Huntington Beach and Laguna Beach. In the summertime there are periodic red tides, and when the water is visibly red, it isn't safe to swim. However, that is when it is nice to visit the beach at night to see glowing blue waves. The red tide creature is a type of dinoflagellate (a single-celled protist) that is also bioluminescent. When agitated, the critters glow or sparkle blue.

In Below the Edge of Darkness: A Memoir of Exploring Light and Life in the Deep Sea, author Edith Widder, PdD tells of the many marine creatures that glow, in many, many ways. In the deep sea, below the limits of sunlight, most animals make their own light. This in itself explains an early mystery: no matter now deep one sent a trawling net, many of the animals brought up had eyes. What are they observing? In this book we learn that there is a lot to observe down there!

Dr. Widder was one of the first persons to descend (in a submersible, of course) into the sea deeper than sunlight can reach, and turn off the lights. Whoever does this for their first time has the same reaction, "It's like a sky full of fireworks!". Yet, just after seeing that, when the lights are turned back on, you typically don't see anything! What gives?

Consider the dinoflagellates that light up the waves along many coastlines. A typical bioluminous dinoflagellate is between 20 and 40 microns in diameter. That's the size of the cells that make up the inside of your cheek. If you use a teaspoon to gently scrape the inside of your cheek, put a drop of the result on a microscope slide and look at medium power, such as 100x, you'll see a bunch of rather blobby cells that appear about an inch across or so, with slightly darker nuclei the size of a BB. Pull the slide out of the microscope and look at it. Just a bit of slightly milky fluid. Nothing you can see distinctly. Yet a single dinoflagellate, the same size as those cheek cells, can make a flash of light that can easily be seen in the dark. Thus, if your sub is surrounded by microbes, you won't see them with the lights on, but in the dark, the flashes they are making because of the disturbance caused by your sub makes the water itself seem to sparkle.

If you so see something, it is likely to be a jellyfish such as this one. Jellyfish and related animals called siphonophores are frequently bioluminescent.

Siphonophores in particular can be so transparent that, even if one is right outside the sub window, you may not see it right away…with the lights on.

What is the purpose of all this light in the deep sea? Three big things, and a host of lesser reasons. The big three: to find food, to avoid being eaten, and to find a mate.

Finding food: Some bioluminescent fish have "flashlights" near their eyes, little organs filled with bioluminescent bacteria, which they feed and care for. The light organs have shutters so the light can be blocked. Many deep sea animals respond to a flash of light with their own flash, so the hunting fish will make a quick flash, and decide among the return flashes if any are worth trying to eat. Whether or not it goes for a meal, it will jerk away, so the flash it made will not let a bigger predator know where it is. Many fish have light organs at the end of appendages where they act as lures to draw in a hungry animal, but it quickly becomes lunch itself. Angler fish are the best known purveyors of this hunting strategy.

Predator avoiding: The flash-and-jerk technique is one way to hunt without being hunted successfully. Another is counter-illumination. Creatures that spend much time near the edge of twilight but not below it could be seen from below unless they employed a little bit of light, shining from their bellies, to mimic the light that would be shining if they weren't there. A similar technique was studied by the U.S. Air Force in the 1970's. A project I worked on briefly studied how well we could see a cluster of lights set against a simulated sky. The idea was to fool the gunners of an antiaircraft battery, who might barely hear a high-flying bomber, but the counter-illumination would make the bomber effectively invisible. It didn't work very well, for two reasons: Firstly, human eyes have very high resolution, so the aircraft would have to have a great many closely-spaced lamps so it wouldn't look like a speckled "something" up above. Secondly, human eyes have excellent color discrimination, and the color of the sky is variable, even varying in different directions at a given time. Thus, lamps of one color that make the plane invisible when seen from directly below, might not work that well to one side or the other. A third nail in the project's coffin: polarizing sunglasses darken the sky, making such an illuminated aircraft more visible than if the lights were left off! Deep-sea fish don't have color vision, and they don't see as clearly, so a cluster of a dozen or two dozen light organs of any bluish or blue-green color, of appropriate brightness, can be an effective invisibility cloak.

Another method to avoid becoming lunch is to make very bright "burglar alarm" flashes when attacked, hoping to bring a bigger predator to drive off or consume whatever is eating you. The Jellyfish Lamp used by Dr. Widder to attract predators in the deep sea emulates a common distress display.

Mate location: Fireflies do this. Those of us living east of the Rockies in the US, and people in many other places worldwide, are familiar with these greenish lights in our yards in June (or December in the southern hemisphere): male fireflies "calling" for females, which don't fly, but rest among vegetation and answer the lights they see with lights of their own. So-called "sea fireflies" (tiny shrimplike ostracods, 1-2 mm long) have a similar mating process, as do a number of other deep water animals. The trick is to make a flash during a turn, to make it harder for a watching predator to locate, similar to hunt-and-jerk.

The last chapters of the book tell the tale of finding and filming giant squids for the first time using a more advanced Jellyfish Lamp named Medusa along with a baitfish to keep the predator busy for a moment. It worked spectacularly well. The montage below shows two images of the attack of a young giant squid on the bait. This squid was "only" ten feet mantle length, with tentacle length estimated at 15-20 feet.

Giant squids that are seen at the surface of the ocean are either dying or dead, and are always red. They float because they have ammonia in their tissues, so they don't need to swim to keep from sinking deeper and deeper. The have to swim to stay down. They are red because they have lost active control of their chromophores. Living, healthy giant squids in the videos these images come from look metallic, with colors of silver and bronze (bronze may indicate alarm), and you can see stripes on the arms.

The videos of these encounters made lots of people very famous, including Dr. Widder. I hope it gives her enough of a platform to advocate more effectively for ocean conservation, along with Sylvia Earle and younger leaders such as Luis David Calderon and Maggie Seida. In her last chapter she tells some compelling stories, including the saga of Georges Bank. This underwater plateau, larger than Massachusetts, has been fished into oblivion. It was once rich with a very diverse ecosystem that included several commercially desirable fish species. Fast-forward a couple of generations. Only after nothing of value was left to catch did the area receive governmental protection. The quantity of life is probably now similar to what existed in the early 1900's, but it is nearly all jellyfish. Not only are the fish gone, including jellyfish-eating swordfish, so are all other jellyfish eaters such as sea turtles. Now that the "cats" are all away, the jelly-mice are out to play, by the trillions. Leaving the place alone may eventually lead to a return to ecological health, but there is a "new normal" at present, and it's pretty stable.

Can we learn enough about the ocean, not just to preserve what's valuable, but to even know what is valuable and needs preserving? The world ocean has been humanity's waste dump and scrounging venue for centuries, even millennia. Now that humans number 8.1 billion, is going back even possible? We spend more on each new NASA venture (all of them much needed!) than the total amount reserved for oceanographic research yearly. A very visible program called Sea Grant has a budget of $90 million. That's "million" with an "M". Compare that to $7.4 billion being spent to "forgive" some student loans. Go ahead, divide the numbers: it's 82 times as much. I'll stop here and let my blood pressure subside.

Whew! I love this book. Get it and read it. Then search "bioluminescence" with your favorite browser and read some more. It can open a new universe to you.